Abstract

We present a convenient and versatile technique to functionalize microfibers by depositing sol-gel jackets via a modified dip-coating method. This was elucidated by gain-functionalizing microfibers with erbium-ytterbium codoped silica sol-gel jackets. For a 4.5-cm-long coated microfiber, an internal gain of 1.8 dB and a net gain of 0.8 dB for a 1550 nm signal were observed, when combing together the gain of the doped jackets and low loss of microfibers. With benefits of convenience and versatility, this technique can be used for functionalizing microfibers with jackets showing gains in other spectral ranges, high nonlinearity, high sensitivity, and many other functions.

Figures (3)

(a) Schematic for sol-gel coating process via a modified dip-coating method. The sol droplet suspended from a syringe scans along the microfiber to deposit thin layers on the surface. Subsequently, the scanning flame used in the taper-drawing process is now employed for a two-step thermal treatment, the first of which is to accelerate the solvent evaporation and the second is to rapidly anneal the sol-gel jacket. The inset shows the cross section of the coated microfiber. (b) The measurement setup of the gain-functionalized microfibers. The pump laser and the signal travel reversely in the microfiber, and optical spectra of the amplified signal are recorded on an optical spectrum analyzer (OSA) (86142b, Agilent). WDM1 and WDM2 were used for separating the 980 and 1550 nm light in our experiment. The isolator before the signal source was used to avoid possible detrimental effects caused by the backward ASE.

(a) Photograph of uniform green up-conversion fluorescence of Er3+ ions in a 4.5-cm-long coated microfiber. (b) Optical spectra of the signal before (blue) and after (black) the sol-gel coating procedure, from which the insertion loss of the jacket was estimated to be less than 1 dB. The cyan and red curves stand for the spectra of ASE and amplified signal, respectively. From these curves, the net gain was estimated to be 0.2 dB.

(a) Optical spectra of the normalized amplified signal at a pump power of 0–500 mW for a 4.5-cm-long coated microfiber. (b) Internal gains and net gains at different pump powers calculated from (a), using a net gain=(Pamplified−PASE)/Pinput and an internal gain=net gain+propagation loss, in which the propagation loss of the jacket was 1 dB (measured at 1310 nm).